The present invention relates to a wire dot print head, and more particularly, to a spring-charged head employing a permanent magnet for shortening the head response time and reducing electric power consumption allowing for high speed printer operation.
U.S. Pat. No. 4,348,120 discloses a spring-charged printer head having a plurality of wire drivers, each driver composed of a permanent magnet, wires, electromagnets and other components. The wire drivers are arranged in a circular pattern. The permanent magnet is ring-shaped and shared by the wire drivers. The wires are fixed to a leaf spring at an angle of about 90.degree.. Using this construction, the head has an increased outside diameter, the head components are complex in shape, and the head cannot be easily assembled.
In addition, since the magnetic circuits for the wires are not separated from each other, there are magnetic interferences between the electromagnets. This causes the wire speeds to vary from each other depending on the numbers of coils being energized. This results in varying printing densities, and sometimes in total printing failures. One solution is to change the coil driving conditions for each printing pattern to yield equal wire speeds. This arrangement, however, requires an expensive apparatus.
There are also limitations on the high-speed operation of the head due to the large inertia of the movable component as well as the increased power consumption and excessive heating of the head. Leaf springs serving as a driving source of the wires are subject to secondary vibrations, thereby causing the wires to move unstably. This has posed a limitation on operation at higher speeds. To cope with this in the conventional art, crossed springs have been employed as wire drive springs. However, these springs are complex in construction, the head cannot be assembled easily, and the cost of the head is increased.